Self-hosted isn’t an option, only Open-Source there. Meaning your Strapi project code needs to publicly available (All Strapi applications are self-hosted, it doesn’t mean that those are open-source or non-profit).
For the OSS option you would include a link to your project code (Git Repo URL). I believe for the “proof of non-profit” you can just include the license.md file you keep in your repo though I’m not sure there.